1. Field of the Invention
The present invention relates to a method for producing a solid-state image pickup device including a photoelectric conversion region for generating and accumulating a carrier by photoelectric conversion.
2. Related Background Art
Recently, a MOS sensor is being employed as a solid-state image pickup device. The MOS sensor has advantages, in comparison with a CCD sensor, of a lower electric power consumption, a lower driving electric power and a high-speed operation. The demand for such MOS sensor is therefore anticipated to grow hereafter.
With such MOS sensor, proposals have been made to expand a dynamic range of the solid-state image pickup device (cf. Japanese Patent Application Laid-open No. 2001-186414, corresponding to U.S. Pat. No. 6,307,195). In such proposal, the MOS sensor is constituted of pixels, each formed for example by a photodiode, a floating diffusion (FD) region, a transfer transistor for transferring a carrier from the photodiode to the FD region, and a reset transistor for resetting the FD region to a predetermined potential, and a plurality of such pixels are arranged in a matrix.
In such MOS sensor, a signal based on a carrier accumulated in the photodiode is read out, and then a signal based on a carrier overflowing from the photodiode and accumulated in the FD region is read, and the read signals are outputted through an analog amplifier.
Also another method has been proposed (cf. Shigetoshi Sugawa et al., “A 100 db Dynamic Range CMOS Image Sensor Using a lateral Overflow Integration Capacitor”, ISSCC 2005/SESSION 19/IMAGES/19.4, DIGEST OF TECHNICAL PAPERS, 2005 IEEE International Solid-State Circuit Conference, Feb. 8, 2005, p 352-353, 603). In the CMOS area sensor in this non-patent reference, a capacitor region of a capacity larger than that of the FD region is formed in each pixel, and a terminal of the capacitor region is connected with the FD region through a switch, while the other terminal of the capacitor region is connected to the ground. Thus, when a strong light causes a carrier overflow from the photodiode, such overflowing carrier is held in the capacitor region to enable a signal output corresponding to the amount of such overflowing carrier, thereby expanding the dynamic range.
However the aforementioned prior technologies, in the solid-state image pickup device provided with pixels having MOS transistors, have not paid at all attention to the aspect of enabling manufacture without complicating the manufacturing process. Therefore, an improvement in the productivity cannot be attained in such solid-state image pickup device.
The present invention has been made in consideration of the aforementioned situation, and an object of the present invention is to provide a producing method for a solid-state image pickup device, capable of simplifying the manufacturing process for a solid-state image pickup device having pixels each including a MOS transistor, thereby realizing an improvement in the productivity of such solid-state image pickup device.